Traditional audio signal level meters use light illumination, with variable intensity and colour, in a vertical illuminated bar to display audio signal level (amplitude/voltage or power) of an audio signal. For example, illumination at the bottom of the meter typically indicates a low signal level. Illumination in the middle of the vertical meter indicates nominal/moderate signal levels. Illumination towards the top of the vertical meter indicates high signal levels. The top of the vertical meter also has a peak warning indication, in the form of a different colour, (just before the audio signal is clipping or peaking at the capabilities of the system). Typical colours associated with signal levels are green for low and moderate/nominal levels. Above nominal is typically yellow and higher signals levels are typically associated with yellow/orange. Peak indication is typically a red illumination. Illumination intensity modulating with signal is also helpful in showing signal behaviour. There are also different variants of meters that are not hardware but are rendered in software, these also use variable colour examples.
There are also meters comprising a single LED (light emitting diode) which shows a different colour to indicate the audio signal level. The single LED may be switched-off to indicate very low signal levels. It may show green for low to nominal/moderate levels, with intensity modulation dependent on the signal to show signal strength in this range. The single LED may show yellow for moderate to high levels, again, with intensity modulation dependent on the signal to show signal strength in this range. Finally, the single LED may show red for high to peaking levels, again, with intensity modulation with the signal to show signal strength in this range.
A single LED meter saves space and enables more compact user interface designs; however, it lacks resolution and can be confusing to use. Also, a single LED meter which provides more information than simply three different colours is preferable.
It is desirable to have a meter that provides higher resolution with greater granularity of information on lower level signals, with potentially less colour variance (which can be confusing on the eye across multiple channels) for nominal level signals, and a clear way of showing a warning of high level signals. Above all, each user wants different things from an audio signal meter and to be alerted to different things. Some users may want more resolution at nominal levels in particular instances. Some may want less resolution at nominal levels in particular instances.